The invention relates generally to machine tools, and, more particularly, to a cutting erosion machine to machine parts of medium to very large size.
Among the machine tools, spark erosion machines are widely used, for example, as cutting or countersink erosion machines. Here a machining tool, in the form of a wire electrode (cutting erosion machine) or a die sinking electrode (die sinking erosion machine), is moved relative to a machining used part which is clamped onto a work table in order to generate an electrical spark discharge between the machining electrode and the machined part. The construction of the machine substantially comprises a machine frame with drive kinematics to generate the relative shifting between the machined part and the machining electrode which determines the machining contour. For this purpose, in the countersink erosion machine, the machining electrode is led by an individual guide head, and, in the case of a cutting erosion machine, from a top wire guide head (first tool guide means) and a second wire guide head (second tool guide means). The machined part or group of machined parts is attached using appropriate clamps on a work table, with the part holding means. For the special case of spark erosion machines, a generator is also provided for the generation and control of the spark discharges, as well as CNC guide and installations for the rinsing of the work slot and the workup of a work fluid, if one is used.
The distinguishing characteristic of cutting erosion machines compared to other conventional machine tools (milling, drilling, circular saw or laser cutting machines, etc.) lies in that the tool (i.e., the wire electrode), must be led on both sides of the machined part (in a first and in a second guide position). This feature is also found, for example, in wire saw machines (for example, diamond wire saws) as well as in belt saw machines, etc. In the case of cutting erosion machines, the two wire guide heads can be moved in different tracks, to generate conical sections. Cutting erosion machines therefore usually have two axes of movement, X and Y (two directions which are orthogonal with respect to each other in a first movement plane) for the generation of the main contour, two axes of movement, U and V, for slanting the wire electrode (two additional directions which are orthogonal with respect to each other in a second movement plane), and a Z axis for the adaptation to the machined part or cutting height.
Machine tools, and especially spark erosion machines, can be used under many circumstances. Therefore, different construction forms have been developed, depending on the specific requirements, such as sales price, maintenance costs, machined part size and maximum displacement path, quality, productivity, flexibility and possibility to automate, space requirements, convenience of operation, etc. The focus in the development of a machine tool can therefore be quite different depending upon its intended application. Frequently such requirements oppose each other (for example, space requirements of the machine on the one hand and maximum possible machined part size, on the other hand). In the last-mentioned case in particular it would be desirable to have as compact a construction design as possible, while still being able to machine larger parts. These requirements are only partly satisfied, for example, in the construction designs for spark erosion machines known to date.
Below, the concepts used in the present description for referring to certain construction designs are explained with reference to special examples in spark erosion machines. Thus, in the case of spark erosion machines, a distinction is made in particular between a C machine frame and a gantry frame. In two special examples of the C machine frame, the horizontal movements are carried out either by the work table, and the electrode guide head performs only the vertical movement (C frame machine), or all horizontal and vertical machine movements are carried out by the electrode guide head (console machine). For this purpose, a so-called cross slide is attached to the machine frame, whose first unit (which is movable with reference to the machine frame) is only suspended or guided at one end on the machine frame. The C frame machine is used in light to medium heavy tool and profile making, while the console machine is used in medium to heavy tool and profile making. The gantry frame presents a higher rigidity and a higher damping capacity than the C machine frame, because the first movable unit is led at both of its ends with respect to the machine frame and, thus, forms the entire gantry. It is preferred, in particular, for very large part and electrode weights. However, it is also used in part in cases where a higher precision is expected.
In principle, the relative movement between the tool and the machined part is carried out either by the movement of the work table, or by the movement of the electrode guide head, or by a combination of the movement of the work table and the movement of the electrode guide head.
In a cutting erosion machine using the gantry construction type, the machine frame generally includes a machine bed and two posts as well as a crossbar arranged on it, forming a gantry carrier. As a result, in comparison to the C frame construction type, a higher rigidity and a more homogeneous expansion are obtained in case of temperature variations. Furthermore, a distinction is made between the machine tools with a rigidly attached gantry carrier and tools with a movable gantry carrier. In fixed gantry machines, a work table (including work containers on the machine bed), is arranged so it can be moved in a main axis direction (for example, the X direction), in a manner of speaking through the gantry carrier. The Y main axis movement of the wire electrode is disengaged therefrom and it is effected by a Y sliding carriage which can be moved horizontally on the crossbar above the work space. The machined part is thus moved in only one axis direction. The machine frame or bed, the posts and cross beams form a unit which is at rest. The lower wire guide head is typically attached by means of an L-shaped lower support arm to the upper Y sliding carriage. This support arm becomes quite long especially with larger machines, and, consequently, due to the long expansion distance, it reacts relatively sensitively to the applications of force and to thermal variations. In addition, installations with a carrier arm designed in that manner take up much space.
Furthermore, so-called gantry machines are known, in which the machined part is at rest during the machining, and the second main axis movement on the machined part is shifted. Here either the entire gantry carrier including the posts is moved with respect to the machine frame in the X main axis direction, or only its crossbar is moved. The advantage of the gantry machines lies in that the weight moved remains constant independently of the machining progress or the part to be machined in each case. Such a cutting erosion machine with movable gantry is known, for example, from DE 20 52 123. An additional example of the gantry construction design, this time in the field of milling machines, is described in EP 0 712 683. Here the two posts are designed in a manner of speaking as walls, and on them guides are arranged for the movement of the cross beam.
A cutting erosion machine is known from U.S. Pat. No. 4,992,640 which has an upper wire guide head in the gantry construction type, a fixed lower wire guide head, and a tool table which can be moved on a cross slide. JP 63-306829 furthermore describes a cutting erosion machine with an upper wire guide head in the gantry construction type, a machined part which is at rest, and a lower wire guide head, which is rigidly coupled, in the gantry construction design, to the upper wire guide head. In this regard, at least one movement of the upper wire guide head (for example, in the X main axis direction), is always coupled rigidly with the movement (for example, in the U direction), of the lower wire guide head. Only the Y main axis movement or the V movement of the two wire guide heads are independent of each other.
Finally, JP 61-34622, JP 61-168426 and JP 61-168424 describe a cutting erosion machine, in which the machined part is at rest, and the upper and lower wire guide heads are each designed as cross sliding carriages which can be moved independently of each other. The drawback of these cross sliding carriage systems is that the external dimensions of the machine are, disadvantageously, very large due to the long movement distances of the cross sliding carriages with respect to the maximum size of the parts to be machined.
This disclosure provides a machine tool wherein the maximum size of the machined part to be machined, or the movement distances are in an advantageous relationship with respect to the external dimensions of the machine tool.
A machine tool is provided which has a machine frame, a first tool guide provided on the machine frame to guide a tool in a first guide position, where the first tool guide is a movable gantry carrier with movable sliding carriage, so that the tool guide, with respect to the machine frame, can be moved in a first plane along a first direction and a second direction which is orthogonal with respect to the first direction a second tool guide provided on the machine frame to guide the tool in a second guide position, where the second tool guide, with respect to the machine frame, can be moved in a second plane along a third direction and a fourth direction which is orthogonal with respect to a third direction, independently of the first tool guide, and a part holder provided on the machine frame to hold the machined part, which is designed in such a manner that the machined part is led between the first and the second guide positions of the tool. The second tool guide is also designed as a movable gantry carrier with movable sliding carriages.